Electrostatic chuck

1. An electrostatic chuck for attracting a flat substrate by an electrostatic force, the electrostatic chuck comprising:

a body including an internal electrode for attracting the flat substrate by the electrostatic force provided therein, the body further including a first surface serving as an electrostatic attraction surface;

a plurality of protrusions formed on the first surface of the body, each protrusion of the plurality of protrusions having a top surface; and

one or more projections positioned on the top surface of each protrusion, and having an outer diameter smaller than the diameter of the protrusion, each of the one or more projections including a mounting surface on which the flat substrate is loaded,

wherein a total area of the mounting surfaces of the one or more projections is equal to or larger than 0.01% and equal to or smaller than 2% of the area of the electrostatic attraction surface,

a height of each projection of the one or more projections from the top surface of each protrusion is in a range equal to or larger than 3 μm and equal to or smaller than 6 μm, and

a sum of a height of a protrusion of the one or more protrusions from the first surface of the body and the height of a projection of the one or more projections is in a range equal to or larger than 30 μm and equal to or smaller than 45 μm.

2. The electrostatic chuck according to claim 1 ,

wherein an area of the mounting surface of each projection is equal to or larger than 2×10 −3 mm 2 and equal to or smaller than 0.8 mm 2 .

3. The electrostatic chuck according to claim 1 ,

wherein an area of the mounting surface of the projection is equal to or larger than 0.05% and equal to or smaller than 50% of the area of the protrusion.

4. The electrostatic chuck according to claim 1 ,

wherein a total area of the plurality of protrusions is equal to or larger than 15% and equal to or smaller than 60% of the area of the electrostatic attraction surface.

5. The electrostatic chuck according to claim 1 , the mounting surface of each projection including a curved portion having a curvature radius in a range of equal to or larger than 0.5 μm and equal to or smaller than 5 μm positioned at a circumference of the mounting surface.

6. The electrostatic chuck according to claim 1 ,

wherein the plurality of protrusions and the one or more projections comprise a composite sintered material of aluminum oxide and silicon carbide that includes equal to or larger than 1% by weight and equal to or smaller than 12% by weight of the silicon carbide, the average diameter of particles of the aluminum oxide being equal to or smaller than 2 μm, and the average diameter of particles of the silicon carbide being equal to or smaller than 0.2 μm.

7. The electrostatic chuck according to claim 1 , further comprising a wall portion provided in a ring shape along a circumference of the electrostatic attraction surface and including a wall top surface configured together with the mounting surfaces of the one or more projections to receive the flat substrate.

8. The electrostatic chuck according to claim 7 ,

wherein the wall top surface includes a step portion along an inner circumference of the wall portion,

wherein the flat substrate is loaded on portions of the wall top surface other than the step portion.

9. The electrostatic chuck according to claim 8 , the step portion comprising one or more second projections, each of the one or more second projections including a second top surface positioned and configured to receive the flat substrate.

10. The electrostatic chuck according to claim 8 , the step portion comprising a second wall portion positioned in a ring shape along a circumference of the step portion, the second wall portion including a second wall top surface positioned and configured to receive the flat substrate.

11. The electrostatic chuck according to claim 10 ,

wherein a height of the second wall portion from the step portion is in a range of equal to or larger than 1 μm and equal to or smaller than 10 μm.